1. Field of the Invention
The present invention relates to improvements in method and apparatus for ultrasonic testing of tubular goods to determine defects, defect orientation and continuity, as well as wall thickness and, more particularly, but not by way of limitation, it relates to improvements in ultrasonic inspection apparatus which enables continuous circumferential testing without rotation of the tubular goods specimen.
2. Description of the Prior Art
The prior art includes various types of apparatus for ultrasonic testing of homogenous material, sheet or rod stock, with some more recent developments attempting such as continuous surface inspection of tubular goods. In most prior art attempts at ultrasonic inspection of tubular goods, it has been necessary to rotate the tubular goods specimen at a prescribed rate relative to its longitudinal movement past ultrasonic testing heads in order to provide complete and reliable surface coverage of the specimen wall or body. Most recently, there have been attempts at full and complete ultrasonic testing of tubular goods at acceptable linear inspection rates without requiring rotation of the specimen. U.S. patent application Ser. No. 242,833 as filed on Mar. 12, 1981 and entitled "Method and Apparatus for Ultrasonic Testing of Tubular Goods" in the name of the present inventor, discloses one form of circumferential testing apparatus wherein each of transverse and longitudinal defects can be ascertained, and periodic wall thickness measurement may be taken as well. The apparatus of U.S. application Ser. No. 242,833 is particularly adapted for on-site inspection of oil well drilling tubular goods during its tripping or vertical attitudes, although the same system is readily adapted for various horizontal testing applications in either field operational or manufacturing facilities.
Other prior art to be considered should include German Pat. No. 28 06 550 as filed on Feb. 16, 1978 as this reference teaches an approach to circumferential ultrasonic inspection utilizing a peripheral alignment of plural ultrasonic sensors with each having sufficient arcuate coverage to provide complete circumferential coverage of the tubular specimen. This is achieved by using two peripheral transducer arrays of equal sectoral coverage but staggered in an equal offset alternating relationship. The pair of arrays may be disposed adjacent one another, but each transducer array must be individually adjusted through a transducer lens and positioning device relative to the particular tubular goods specimen. If both transverse and longitudinal defect detection is desired, then it is necessary to align and adjust a separate pair of circumferential arrays for each of the selected defect characteristics. This reference contemplates no specific electronic apparatus for futher differentiating types of defects or for wall thickness considerations.
British Pat. No. 2,027,199 (A) teaches the use of a number of precision ground convex ancillary lenses that are each focused in a highly restricted area. Pairs of transducers with lenses may be used in a pitch-catch mode such that a greater number of transducers are required to provide complete circumferential coverage. The specific teaching of the patent for testing up to 10 centimeter tube diameters uses six pitch/catch transducers in a peripheral array, and at least four such peripheral arrays are aligned in longitudinal juxtaposition but incrementally circumferentially offset each to the other in order to provide complete coverage. While mention is made that transverse defects and wall thickness measurements are possible, no teaching or alternative suggestions are present. Finally, yet another pitch/catch mode of circumferential tubular goods inspection is present in a publication entitled "A High-Speed Ultrasonic Testing Machine for Tubes", The Radio and Electronic Engineer, Volume 41, No. 5, May 1971, in the name of Kyte and Whittington. This teaching uses a series of identical probes arranged in a ring encircling the tubular goods, each individual energy path including a transmitter and receiver position, and fast sequential pulsing of the probes together with slow rotation of the tube will enable effective circumferential scanning. This teaching contemplates both twin-probe or pitch/catch mode and the transceiver mode of operation but there is still required the rotation of the tubular specimen, albeit at a slow rate. Also, utilizing the disclosed forms of array, it is emphasized that the outer limit of ultrasonic transducer employment in the single system would be less than 72, and that the largest tube size for practical application of testing is less than four inches outside diameter.